Prior art power transmissions have been provided utilizing planetary gear sets and clutches which can be configured so that accessories normally operated by an internal combustion engine can be driven by an electric motor/generator; see U.S. Pat. No. 5,558,173 issued Sep. 24, 1996 and commonly assigned as this application. As in most prior art designs, accessories are driven through belt connections to the internal combustion engine. Such accessories have included oil pumps, power steering pumps and transmission oil pumps. Because such pumps are generally belt-driven from the internal combustion engine, they idle when the engine is not running.
There are current applications that use an electric oil pump in hybrid transmission applications, but they tend to be stand alone pumps with pump rotor and electric motor, i.e., a full function electric oil pump. And the integration of a separate electric oil pump with the hydraulic control circuit of the transmission presents challenges such as providing a suction feed and a pressure feed back into the transmission.
An oil pump driving device has been used to drive an oil pump combined with a transmission coupled to an engine for supplying working oil to lubricate the transmission and enable the transmission to make gear shifts; see U.S. Pat. No. 5,474,428 to Kimura et al. issued Dec. 12, 1995. The transmission includes a first power transmitting mechanism for connecting the output shaft of an electric motor to the drive shaft of the oil pump, and a second power transmitting path for connecting the output shaft of the engine to the drive shaft of the oil pump. A controller for selecting one of the first and second power transmitting mechanisms at a time selects the first transmitting mechanism to drive the oil pump with the electric motor when the rotational speed of the output shaft of the engine is lower than a predetermined speed, and selects the second power transmitting mechanism to drive the oil pump with the engine when the rotational speed of the output shaft of the engine exceeds the predetermined speed. But such oil pump arrangements use a gear pump, two one-way clutches, and a controller to select the clutch.